Automated envelope tracking system

ABSTRACT

Embodiments described herein relate to an envelope tracking system that uses a single-bit digital signal to encode an analog envelope tracking control signal, or envelope tracking signal for brevity. In certain embodiments, the envelope tracking system can estimate or measure the amplitude of the baseband signal. The envelope tracking system can further estimate the amplitude of the envelope of the RF signal. The system can convert the amplitude of the envelope signal to a single-bit digital signal, typically at a higher, oversample rate. The single-bit digital signal can be transmitted in, for example, a low-voltage differential signaling (LVDS) format, from a transceiver to an envelope tracker. An analog-to-digital converter (ADC or A/D) can convert the single-bit digital signal back to an analog envelope signal. Moreover, a driver can increase the power of the A/D output envelope signal to produce an envelope-tracking supply voltage for a power amplifier.

RELATED APPLICATIONS

This disclosure claims priority to U.S. Provisional Application No.62/272,958, which was filed on Dec. 30, 2015 and is titled “AUTOMATEDENVELOPE TRACKING SYSTEM,” the disclosure of which is expresslyincorporated by reference herein in its entirety for all purposes. Anyand all applications, if any, for which a foreign or domestic priorityclaim is identified in the Application Data Sheet of the presentapplication are hereby incorporated by reference in their entiretiesunder 37 CFR 1.57.

BACKGROUND Technical Field

This disclosure relates to an automated envelope tracking system.

Description of Related Technology

Wireless device manufacturers continue to add new features to wirelessdevices (e.g., smartphones). Often, the new features will cause areduction in the battery life of the wireless device. This reduction inbattery life is in direct opposition to many users' desire for longerbattery life.

As users move in relation to a wireless base station, the amount ofpower for maintaining a communication connection with the wireless basestation may vary. Often, a wireless device may use a particular amountof power to ensure that the communication connection is maintainedregardless of the distance to the base station within a particular rangeof the base station. One element in the wireless device that may requiredifferent amounts of power based on its distance to the base station isthe power amplifier that processes the radio frequency signal fortransmission.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers are re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate embodiments of the inventive subject matter described hereinand not to limit the scope thereof.

FIG. 1 illustrates a block diagram of a power amplifier module foramplifying a radio frequency (RF) signal.

FIG. 2 illustrates a block diagram of an example wireless device thatcan include one or more of the power amplifier modules of FIG. 1.

FIGS. 3A-3B illustrate two examples of a power amplifier supply voltageversus time.

FIG. 4 is a block diagram of an embodiment of a communication subsystemincluding a transceiver and a front-end module (FEM).

FIG. 5 is a more detailed block diagram of an embodiment of thecommunication subsystem of FIG. 4.

FIG. 6 is another block diagram of an embodiment of the communicationsubsystem introduced in FIG. 4.

FIG. 7 illustrates a block diagram of one embodiment of a transceiverpaired with multiple front end modules.

FIGS. 8A and 8B present two flowcharts relating to envelope-trackingsupply voltage processes.

FIG. 9 presents a graph of one example of delta sigma modulator outputvoltage and a corresponding envelope tracker output voltage versus time.

FIG. 10 presents a graph of an example envelope tracker output voltageand a corresponding theoretically ideal output voltage versus time.

FIG. 11 presents a graph of an example envelope tracker output spectraldensity and a corresponding theoretically ideal output spectral densityversus spectral density requirement of a communication scheme.

SUMMARY

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for theall of the desirable attributes disclosed herein. Details of one or moreimplementations of the subject matter described in this specificationare set forth in the accompanying drawings and the description below.

Certain aspects of the present disclosure relate to an envelope trackingsystem. The envelope tracking system can include a signal measuringdevice configured to determine a size of a radio frequency input signal.Further, the envelope tracking system may include a bit-encoderconfigured to encode an envelope tracking control signal to obtain anencoded envelope tracking control signal. The envelope tracking controlsignal may be based at least in part on the size of the radio frequencyinput signal. In addition, the envelope tracking system may include anenvelope tracker configured to provide a supply voltage to a poweramplifier. The supply voltage may be based at least in part on theencoded envelope tracking control signal.

The signal measuring device may determine the size of the radiofrequency input signal by determining an amplitude of an I and Qcomponent of a baseband signal associated with the RF input signal.Determining the amplitude of the radio frequency input signal mayinclude obtaining the absolute value of the amplitude of the I and Qcomponents associated with the RF input signal.

In some implementations, the signal measuring device implements acoordinate rotation digital computer algorithm. Further, the bit-encodermay include a sigma-delta modulator. The envelope tracking system mayalso include a lookup table storing a plurality of envelope trackingcontrol values. The envelope tracking control signal may be generatedbased at least in part on the size of the radio frequency input signalor a selection of an envelope tracking control value from the pluralityof envelope tracking control values.

The envelope tracking system may also include a pair of low-voltagedifferential signaling lines configured to communicate the encodedenvelope tracking control signal from the bit-encoder to the envelopetracker. Further, the envelope tracker may include a digital to analogconverter configured to convert the encoded envelope tracking controlsignal to an analog signal. In addition, the envelope tracker mayinclude a driver configured to generate the supply voltage. The size ofthe radio frequency input signal may include an instantaneous amplitudeof the radio frequency input signal.

Certain embodiments of the present disclosure relate to a wirelessdevice. The wireless device may include a transceiver and a front-endmodule. The transceiver may include a signal measuring device and abit-encoder. The signal measuring device may be configured to determinea size of a radio frequency input signal. The bit-encoder may beconfigured to encode an envelope tracking control signal to obtain anencoded envelope tracking control signal. The envelope tracking controlsignal may be based at least in part on the size of the radio frequencyinput signal. The front-end module may be in communication with thetransceiver. Further, the front-end module may include an envelopetracker configured to provide a supply voltage to a power amplifier. Thesupply voltage may be based at least in part on the encoded envelopetracking control signal.

Some implementations of the wireless device may include a plurality offront-end modules. At least some of the front-end modules may includeone or more power amplifiers configured to process signals of differentfrequency bands than at least some other of the front-end modules. Theplurality of front-end modules may be in communication with thetransceiver via a plurality of pairs of low-voltage differentialsignaling lines. At least one of the pairs of low-voltage differentialsignaling lines may be of a different length than at least one otherpair of low-voltage differential signaling lines.

In some embodiments, the bit-encoder includes a sigma-delta modulator.Moreover, the transceiver may further include a non-volatile storageconfigured to store a mapping of a plurality of radio frequency inputsize values to a plurality of envelope tracking control values. Theenvelope tracking control signal may be determined based at least inpart on the size of the radio frequency input signal and the mapping ofthe plurality of radio frequency input size values to the plurality ofenvelope tracking control values. In some cases, the envelope trackerincludes a digital to analog converter configured to convert the encodedenvelope tracking control signal to an analog signal. Further, theenvelope tracker may include a driver configured to modify a voltagereceived from a battery to obtain the supply voltage for the poweramplifier.

Certain aspects of the present disclosure relate to a method ofenvelope-tracking a radio frequency signal. The method may includereceiving I and Q components of a radio frequency signal and determiningan expected size of the radio frequency signal based on a measurement ofthe I and Q components. Further, the method may include determining acontrol signal based at least in part on the expected size of the RFsignal. The control signal may indicate a voltage envelope for the radiofrequency signal. In addition, the method may include converting thecontrol signal to a low-voltage differential signaling format using asingle-bit encoder to obtain an encoded control signal. The method mayfurther include providing the encoded control signal to an envelopetracker. In some embodiments, in response to providing the encodedcontrol signal to the envelope tracker, the method may further includemodifying a device supply voltage based at least in part on the encodedcontrol signal and providing the modified device supply voltage to apower amplifier that receives the radio frequency signal.

DETAILED DESCRIPTION

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.For the purpose of the present disclosure, the terms mobile devices andwireless devices are used interchangeably.

Introduction

Power amplifiers can be included in mobile or wireless devices toamplify radio frequency (RF) signals for transmission via one or moreantennas. For example, in mobile devices using frequency divisionduplexing (FDD), such as systems using long term evolution (LTE), apower amplifier can be used to amplify one or more transmit carrierfrequencies. It can be important to manage RF signal amplification tomaintain transmission range and to conserve battery life. A desiredtransmit power level can depend on the mobile environment and/or auser's distance from a base station.

With the constant desire for longer battery life, the power consumptionof a power amplifier can be an important consideration. One techniquefor reducing power consumption of a power amplifier is the use ofenvelope tracking, which can include controlling a supply voltage of thepower amplifier relative to the envelope of the RF signal or signalenvelope. Thus, when a voltage level of the signal envelope increases,the voltage level of the power amplifier supply voltage can beincreased. Likewise, when the voltage level of the signal envelopedecreases, the voltage level of the power amplifier supply voltage canbe decreased to reduce power consumption.

The use of envelope tracking can create a timing requirement on thesystem. Specifically, the supply voltage should track the RF signalenvelope in the time domain to avoid introducing degradation to the RFsignal due, for example, to clipping of the RF signal. Clipping of theRF signal may occur when the RF signal has a higher voltage than thesupply voltage. The RF signal may have a higher voltage than the supplyvoltage, for example, when the RF signal envelope increases in voltagemore than the increase in supply voltage due to a lag in tracking the RFsignal envelope voltage.

The demand for higher data rates in mobile and wireless communicationdevices has created technical challenges for power amplifier systems.For example, certain mobile devices operate using carrier aggregation inwhich the mobile device communicates across multiple carriers, which canbe in the same frequency band or in different frequency bands. Althoughcarrier aggregation can increase bandwidth, carrier aggregation can haverelatively stringent power amplifier linearity specifications.Furthermore, certain mobile devices can operate over a wide range offrequencies, including high frequency bands in which power amplifiersmay exhibit relatively poor linearity.

In some cases, the demand for higher date rates in mobile and wirelesscommunication devices can be addressed using Multiple Input MultipleOutput (MIMO) systems with spatially separated diversity antennas. Toreduce RF interference, a power amplifier is typically placed in closeproximity to the antenna connected to the power amplifier. In some MIMOsystems, spatially separated antennas may result in spatially separatedpower amplifiers. In a conventional design, the spatially separatedpower amplifiers may share the same sources of RF signals and analogenvelope-tracking signals from a single transceiver. The spatialseparation of the power amplifiers can cause differences in propagationlengths or delays and in frequency responses of the transmission pathsbetween the single transceiver and the plurality of power amplifiers.These differences can become even more pronounced at the high bandwidthsthat may be used to support high data rates. Left uncompensated for,these differences can result in distortions in the amplified RF signalproduced, for example, by the clipping effect described above. Thisreduced RF signal integrity can degrade communication system performance(for example, by increasing a RF channel's out-of-band emission) and cancause the system to fall short of the requirements imposed by acommunication standard. Thus, in some cases, analog envelope-trackingsignals generated by a transceiver with a conventional envelope trackingsystem often need to be calibrated to compensate for the differences insignal distortions created by the different frequency responses and pathdelays to the different power amplifiers. Furthermore, frequencyresponse and path delays may limit the bandwidth of a conventionalenvelope tracking system to 40 MHz, as an example.

Although the above description uses a MIMO system to illustrate sometechnical challenges to the design of envelope tracking systems, atleast some of these technical challenges may also occur in Single InputSingle Output (SISO) systems. In other words, regardless of the numberof power amplifiers in the system, delay and/or degradation of the RFsignal may occur between a transceiver and a power amplifier.

Embodiments described herein relate to an envelope tracking system thatuses a single-bit digital signal to encode an analog envelope trackingcontrol signal, or envelope tracking signal for brevity. In certainembodiments, the envelope tracking system can estimate or measure theamplitude of the baseband signal. The envelope tracking system canfurther estimate the amplitude of the envelope of the RF signal. Thesystem can convert the amplitude of the envelope signal to a single-bitdigital signal, typically at a higher, oversample rate. The single-bitdigital signal can be transmitted in, for example, a low-voltagedifferential signaling (LVDS) format, from a transceiver to an envelopetracker. An analog-to-digital converter (ADC or A/D) can convert thesingle-bit digital signal back to an analog envelope signal. Moreover, adriver can increase the power of the A/D output envelope signal toproduce an envelope-tracking supply voltage for a power amplifier.

Advantageously, in certain embodiments, because transmitting asingle-bit digital signal from a transceiver to a power amplifier modulegenerally does not suffer from the limitations associated withtransmitting a high-bandwidth analog signal, embodiments according tothe present disclosure can support an envelope-tracking signal withbandwidth up to or exceeding 300 MHz. In contrast, many conventionalsystems are limited to bandwidths of 40 MHz or less for theenvelope-tracking signal.

Example Power Amplifier Module

FIG. 1 is a block diagram of a power amplifier module (PAM) 10 foramplifying a radio frequency (RF) signal. The illustrated poweramplifier module 10 amplifies an RF signal (RF_IN) to generate anamplified RF signal (RF_OUT). As described herein, the power amplifiermodule 10 can include one or more power amplifiers.

Example Wireless Device

FIG. 2 is a block diagram of an example wireless or mobile device 11that can include one or more of the power amplifier modules 10 ofFIG. 1. The wireless device 11 can also include an envelope trackingsystem implementing one or more features of the present disclosure.

The example wireless device 11 depicted in FIG. 2 can represent amulti-band and/or multi-mode device such as a multi-band/multi-modemobile phone. By way of examples, Global System for Mobile (GSM)communication standard is a mode of digital cellular communication thatis utilized in many parts of the world. GSM mode mobile phones canoperate at one or more of four frequency bands: 850 MHz (approximately824-849 MHz for Tx, 869-894 MHz for Rx), 900 MHz (approximately 880-915MHz for Tx, 925-960 MHz for Rx), 1800 MHz (approximately 1710-1785 MHzfor Tx, 1805-1880 MHz for Rx), and 1900 MHz (approximately 1850-1910 MHzfor Tx, 1930-1990 MHz for Rx). Variations and/or regional/nationalimplementations of the GSM bands are also utilized in different parts ofthe world.

Code division multiple access (CDMA) is another standard that can beimplemented in mobile phone devices. In certain implementations, CDMAdevices can operate in one or more of 800 MHz, 900 MHz, 1800 MHz and1900 MHz bands, while certain W-CDMA and Long Term Evolution (LTE)devices can operate over, for example, 22 or more radio frequencyspectrum bands.

One or more features of the present disclosure can be implemented in theforegoing example modes and/or bands, and in other communicationstandards. For example, 802.11, 2G, 3G, 4G, LTE, and Advanced LTE arenon-limiting examples of such standards. To increase data rates, thewireless device 11 can operate using complex modulated signals, such as64-QAM signals.

In certain embodiments, the wireless device 11 can include switches 12,a transceiver 13, an antenna 14, power amplifiers 17 a, 17 b, a controlcomponent 18, a computer readable medium 19, a processor 20, a battery21, and an envelope tracker 30.

The transceiver 13 can generate RF signals for transmission via theantenna 14. Furthermore, the transceiver 13 can receive incoming RFsignals from the antenna 14.

It will be understood that various functionalities associated with thetransmission and reception of RF signals can be achieved by one or morecomponents that are collectively represented in FIG. 2 as thetransceiver 13. For example, a single component can be configured toprovide both transmitting and receiving functionalities. In anotherexample, transmitting and receiving functionalities can be provided byseparate components.

Similarly, it will be understood that various antenna functionalitiesassociated with the transmission and reception of RF signals can beachieved by one or more components that are collectively represented inFIG. 2 as the antenna 14. For example, a single antenna can beconfigured to provide both transmitting and receiving functionalities.In another example, transmitting and receiving functionalities can beprovided by separate antennas. In yet another example, different bandsassociated with the wireless device 11 can operate using differentantennas.

In FIG. 2, one or more output signals from the transceiver 13 aredepicted as being provided to the antenna 14 via one or moretransmission paths 15. In the example shown, different transmissionpaths 15 can represent output paths associated with different bandsand/or different power outputs. For instance, the two example poweramplifiers 17 a, 17 b shown can represent amplifications associated withdifferent power output configurations (e.g., low power output and highpower output), and/or amplifications associated with different bands.Although FIG. 2 illustrates a configuration using two transmission paths15 and two power amplifiers 17 a, 17 b, the wireless device 11 can beadapted to include more or fewer transmission paths 15 and/or more orfewer power amplifiers. In the remainder of the disclosure, a poweramplifier in a wireless device may be individually referred to as poweramplifier 17 a, power amplifier 17 b, etc., or may be individually orcollectively referred to as power amplifier(s) 17.

In FIG. 2, one or more detected signals from the antenna 14 are depictedas being provided to the transceiver 13 via one or more receiving paths16. In the example shown in FIG. 2, different receiving paths 16 canrepresent paths associated with different bands. For example, the fourexample receiving paths 16 shown can represent quad-band capability withwhich some wireless devices are provided. Although FIG. 2 illustrates aconfiguration using four receiving paths 16, the wireless device 11 canbe adapted to include more or fewer receiving paths 16.

To facilitate switching between receive and transmit paths, the switches12 can be configured to electrically connect the antenna 14 to aselected transmit or receive path. Thus, the switches 12 can provide anumber of switching functionalities associated with operation of thewireless device 11. In certain embodiments, the switches 12 can includea number of switches configured to provide functionalities associatedwith, for example, switching between different bands, switching betweendifferent power modes, switching between transmission and receivingmodes, or some combination thereof. The switches 12 can also beconfigured to provide additional functionality, including filteringand/or duplexing of signals.

FIG. 2 shows that in certain embodiments, a control component 18 can beprovided for controlling various control functionalities associated withoperations of the switches 12, the power amplifiers 17 a, 17 b, theenvelope tracker 30, and/or other operating components.

In certain embodiments, a processor 20 can be configured to facilitateimplementation of various processes described herein. The processor 20can implement various computer program instructions. The processor 20can be a general purpose computer, special purpose computer, or otherprogrammable data processing apparatus.

In certain embodiments, these computer program instructions may also bestored in a computer-readable memory 19 that can direct the processor 20to operate in a particular manner, such that the instructions stored inthe computer-readable memory 19.

The illustrated wireless device 11 also includes the envelope tracker30, which can be used to provide power amplifier supply voltages to oneor more of the power amplifiers 17 a, 17 b. For example, the envelopetracker 30 can be configured to change the supply voltages provided tothe power amplifiers 17 a, 17 b based upon an envelope of the RF signalto be amplified. In the illustrated implementation, the envelope signalis provided to the envelope tracker 30 from the transceiver 13. However,other implementations are possible, including, for example,configurations in which the envelope signal is provided to the envelopetracker 30 from a baseband processor or a power management integratedcircuit (PMIC). Furthermore, in certain implementations, the envelopesignal can be generated from the RF signal by detecting the RF signal'senvelope using any suitable envelope detector.

The envelope tracker 30 can be electrically connected to the battery 21,which can be any suitable battery for use in the wireless device 11,including, for example, a lithium-ion battery. As will be described indetail further below, by controlling the voltage provided to one or moreof the power amplifiers 17 a, 17 b, the power consumed from the battery21 can be reduced, thereby improving the battery life of the wirelessdevice 11. In certain configurations, the power amplifiers 17 a, 17 bcan be implemented using CMOS processing, which can lower cost and/orenhance integration. However, other configurations of the poweramplifiers 17 a, 17 b are possible. For example, the power amplifiers 17a, 17 b can be implemented using III-V semiconductor processing, such asGallium Arsenide (GaAs) processing.

In certain configurations, the wireless device 11 may operate usingcarrier aggregation. Carrier aggregation can be used for both FrequencyDivision Duplexing (FDD) and Time Division Duplexing (TDD), and may beused to aggregate a plurality of carriers or channels, for instance upto five carriers. Carrier aggregation includes contiguous aggregation,in which contiguous carriers within the same operating frequency bandare aggregated. Carrier aggregation can also be non-contiguous, and caninclude carriers separated in frequency within a common band or indifferent bands.

Example Power Amplifier Supply Voltage Signals

FIGS. 3A-3B show two examples of power amplifier supply voltage versustime. In FIG. 3A, a graph 300 illustrates one example of the voltage ofan RF signal 302 and a power amplifier supply voltage 306 versus time.The RF signal 302 has an envelope 304.

It can be important that the power amplifier supply voltage 306 of apower amplifier has a voltage greater than that of the RF signal 302.For example, powering a power amplifier using a power amplifier supplyvoltage that has a magnitude less than that of the RF signal can causethe RF signal to be clipped, thereby creating signal distortion and/orotherwise degrading signal integrity. Thus, it can be important that thepower amplifier supply voltage 306 be greater than that of the envelope304. However, it can be desirable to reduce a difference in voltagebetween the power amplifier supply voltage 306 and the envelope 304 ofthe RF signal 302, as the area between the power amplifier supplyvoltage 306 and the envelope 304 can represent lost energy, which canreduce battery life and increase heat generated in a wireless device.

In FIG. 3B, a graph 310 illustrates another example of the voltage of anRF signal 302 and a power amplifier supply voltage 308 versus time. Incontrast to the power amplifier supply voltage 306 of FIG. 3A, the poweramplifier supply voltage 308 of FIG. 3B changes in relation to theenvelope 304 of the RF signal 302. The area between the power amplifiersupply voltage 308 and the envelope 304 in FIG. 3B is less than the areabetween the power amplifier supply voltage 306 and the envelope 304 inFIG. 3A, and thus the graph 310 of FIG. 3B can be associated with apower amplifier system having greater energy efficiency.

Example Envelope Tracking System

FIG. 4 illustrates a block diagram of one embodiment of a communicationsubsystem 400 including an envelope tracking system 432. The illustratedcommunication subsystem 400 includes a transceiver 13 and an envelopetracking front end module (ET FEM) 430. The illustrated transceiver 13includes a baseband processor 402, an I/Q modulator 404, a signalestimation component 412, an envelope-shaping look-up table (LUT) 414, adelta-sigma modulator 416, and a clock 418. The delta-sigma modulator416 and the clock 418 may together be referred to as a bit encoder. Asillustrated, the signal estimation component 412 may implement a vectorlength function or an absolute value function to calculate the magnitudeof the baseband I/Q signals. This absolute value function forcalculating the baseband I/Q signals may include calculating the squareroot of the I/Q components squared: sqrt(I^2+Q^2). The signal estimationcomponent and the envelope-shaping LUT may together be referred to as asignal measuring device.

Further, the illustrated ET FEM includes a power amplifier 17 a, a 1-bitdigital-to-analog converter (DAC or D/A) 422, and a driver 424. Thesignal estimation component 412, e.g., an absolute value function, thelook-up table (LUT) 414, the delta-sigma modulator 416, the clock 418,the 1-bit D/A 422, and the driver 424 may be included as components ofthe envelope tracking system 432. The 1-bit D/A 422 and the driver 424may be included as portions of the envelope tracking system 432 withinthe ET FEM 430 and are collectively designated as an envelope tracker434.

The baseband processor 402 can be used to generate an I signal componentand a Q signal component of a baseband signal. The I and Q signalcomponents can be used to represent a sinusoidal wave or signal of adesired amplitude, frequency, and phase. For example, the I signal canbe used to represent an in-phase component of the sinusoidal wave andthe Q signal can be used to represent a quadrature component of thesinusoidal wave. The composite of I and Q signals can be an equivalentrepresentation of the sinusoidal wave. In certain implementations, the Iand Q signals can be provided to the I/Q modulator 404 in a digitalformat. The baseband processor 402 can be any suitable processorconfigured to process a baseband signal. For instance, the basebandprocessor 402 can include a digital signal processor, a microprocessor,a programmable core, or any combination thereof. Moreover, in someimplementations, two or more baseband processors 402 can be included inthe communication subsystem 400.

The I/Q modulator 404 can be configured to receive the I and Q signalsfrom the baseband processor 402 and to process the I and Q signals togenerate an RF signal based on the received baseband signal. Forexample, the I/Q modulator 404 can include one or more DACs configuredto convert the I and Q signals into an analog format, mixers forupconverting the I and Q signals to radio frequency signals, and asignal combiner for combining the upconverted I and Q signals into an RFsignal that can be amplified by the power amplifier 17 a. Thus, the I/Qmodulator 404 may function as an upconverter and may convert a basebandsignal into the RF signal. In certain implementations, the I/Q modulator404 can include one or more filters configured to filter frequencycontent of signals processed therein.

The RF signal produced by the I/Q modulator 404 is output from thetransceiver 13 to the ET FEM 430, which provides the RF signal to thepower amplifier 17 a. In some cases, the output of the I/Q modulator 404is provided to a radio frequency (RF) driver 440 that amplifies the RFsignal before providing it to the ET FEM 430. This RF driver 440 mayinclude one or more transistors or power amplifiers that can be used toamplify the RF signal. Amplifying the RF signal helps to maintain thesignal integrity as it is transmitted to the ET FEM 430. This isparticularly important in embodiments where the ET FEM 430 is notdirectly adjacent to the transceiver 13. The transceiver 13 and the ETFEM 430 may be spatially separated due to space constraints in thedevice. They may also be separated due to the desire to separatecorresponding antennas of the ET FEMs in a multiple antenna device. Itis generally desirable to separate the plurality of antennas to reducesignal interference between signals received or transmitted by thedifferent antennas. The power amplifier 17 a may amplify the RF signalto a power level sufficient to reach a selected destination (e.g., abase station) with adequate signal integrity (e.g., signal integritythat satisfies a signal integrity threshold of, for example, the basestation).

The signal estimation component 412 can perform one or more processesfor measuring characteristics of the I and Q components of the basebandsignal, such as measuring the magnitude of the signal components. Thebaseband signal may include a signal that extends from 0 up to aparticular frequency. In contrast, the RF signal may be associated witha lower frequency and a higher frequency, but may not extend to DC. Thebaseband signal may represent the envelope signal for transmitting an RFsignal.

To measure signal magnitude, the signal estimation component may beimplemented as any system that can determine an approximate magnitude ofthe baseband I/Q signals. FIG. 4 illustrates the signal estimationcomponent 412 implemented as a vector length function. The signalestimation component 412 may, for example, estimate the magnitude of thebaseband I/Q signals by using floating-point or fixed-point arithmeticto compute the square root of (I²+Q²). The square root computation, inturn, may be implemented in a variety of ways. For example, a look-uptable may be used to derive the square root of a fixed-point number.Alternatively, a Taylor series of an arbitrary length may be used tocompute a square root. A person of ordinary skill in the art willappreciate that a system that can determine the magnitude of thebaseband I/Q signals to varying degrees of accuracy may be used as asignal estimation component 412 in the place of the absolute value orvector length function illustrated in FIG. 4.

The envelope-shaping look-up table (LUT) 414 can be used to convert amagnitude signal associated with the I and Q signals (e.g., the outputof the signal estimation component) into a shaped envelope signal.Shaping may be used to map amplitude values of the input signal to aselected voltage. Alternatively, a polynomial function could be used toobtain the same or a similar effect as shaping the signal. Shaping theenvelope signal from the baseband processor 402 can aid in enhancingperformance of the communication subsystem 400. As illustrated in FIG.4, the envelope-shaping look-up table (LUT) 414 comprises a look-uptable, such as a programmable memory, configured to generate a digitalshaped envelope signal which can be converted into an analog shapedenvelope signal for supply to the power amplifier 17 a. The look-uptable can store a plurality of baseband I/Q magnitude values and thecorresponding envelope tracking control signal values. The look-up tablecan receive a digital input signal indicating a voltage level of themagnitude signal (e.g. output of the signal estimation component 412),and can generate a digital output signal indicating a voltage level ofthe envelope signal. The look-up table may be stored in a non-volatilestorage. However, a shaped envelope signal can be generated via meansother than a look-up table or a look-up table with baseband I/Q signalmagnitude-to-envelope mapping. For example, it is feasible, in somecases, to use the output of I/Q modulator 404 as input to the look-uptable 414. Alternatively, it is feasible to generate an envelope signalby low-pass filtering the output of I/Q modulator 404 without the use ofa look-up table 414.

The mapping stored in the look-up table 414, e.g., a plurality ofbaseband I/Q magnitude values and the corresponding envelope trackingcontrol signal values, may be dependent on the RF frequency of the RFsignal. Thus, the look-up table 414 may include multiple tables wherethe communication subsystem 400 may transmit in one of a plurality of RFfrequencies.

The delta-sigma modulator 416 applies delta-sigma modulation to theenvelope signal output from LUT 414 to encode the envelope signal usinga single bit. This single-bit output can be a representation of thepolarity of the slope of the envelope signal at the time of thedelta-sigma sampling time. For example, if the envelope signal isincreasing in amplitude (e.g., the slope is positive), the output of thedelta-sigma modulator 416 may be set to a supply voltage of thetransceiver (not shown). If the envelope signal is decreasing inamplitude (e.g., slope is negative), the output of the delta-sigmamodulator 416 may be set to zero volts or a minimum voltage. As anotherexample, if the envelope signal is neither increasing nor decreasing inamplitude at the sampling time, the output of the delta-sigma modulator416 may remain at the same value from the last sampling period. Thoughnot shown in FIG. 4, the output of the delta-sigma modulator 416 can bean input to a component which converts the output of the delta-sigmamodulator 416 to the LVDS format.

The clock 418 can provide the clock signal at which the delta-sigmamodulator 416 operates. In some cases, to represent an envelope-trackingsignal using one bit resolution, the delta-sigma modulator 416 mayoperate at an oversample clock rate. For example, the oversample clockrate may be ten to fifteen times the bandwidth of the envelope signal orthe corresponding RF signal. For instance, the envelope-tracking signalmay be sampled at 200 mega-samples per second (Msps) to generate anenvelope-tracking signal with 20 MHz bandwidth at the output of envelopetracking system 432.

The transceiver 13 outputs the output signal of delta-sigma modulator416 in LVDS format on lines 420. The LVDS format uses digitaldifferential signals, hence each signal may be transferred to the ET FEM430 on one line of a pair of lines. The information transmitted on thelines 420 may then be determined based on a voltage difference betweenthe two lines.

It should be understood that LVDS is one non-limiting example forrepresenting the envelope information and for providing the envelopeinformation to the ET FEM 430. Other systems and methods for encoding ortransmitting the envelope information are possible. These other methodsmay also maintain the digital format of the signals. For example, insome implementations, the LVDS lines 420 can be replaced with a singlewire interface. This single wire interface can be used as a serialinterface. Further, the single wire interface can combine a clock anddata signal on a single line. For example, the data can be encoded onthe line by modifying the frequency of the clock signal. Alternatively,the data can be encoded by adjusting the amplitude of the clock signalwhile maintaining the clock frequency. Although providing the clocksignal is possible, it is generally not desired because it can create anoise source on the clock signal of the transceiver 13. The clock signalcan generate a high power tone, which may be upconverted and producenoise. By using a delta-sigma modulator, the clock noise can be spreadout minimizing its impact.

Another alternative to using the LVDS lines is to use a non-return tozero signal over the single line. In such an implementation, the clockmay be implicit with the data because, for example, every bit is clockedone clock period. These alternative options are noisier than using asigma-delta bit stream as used by embodiments disclosed herein. Usingthe sigma delta bit stream, the clock is not transmitted, but may berecovered by the ET FEM 430.

While the illustrated embodiments using a 1-bit encoder, it should beunderstood that the present disclosure is not limited as such. Forexample, multiple pairs of LVDS lines may be between the transceiver 13and the ET FEM 430 enabling the transmission of multiple bits. In suchcases, the ET FEM 430 may include multiple 1-Bit D/As 422 or the D/A 422may support multiple bits. In other embodiments, the lines between thetransceiver 13 and the ET FEM 430 may be configured to provide multiplebits by, for example, using multiple amplitude levels to representdifferent digital values.

Advantageously, in certain embodiments, interference produced by thedigital LVDS signals on lines 420 may cause less degradation to the RFsignal than an analog envelope signal transmitted from a transceiver toan FEM. The lower degradation may occur because, in some cases, thedigital LVDS signals on lines 420 operate at a much higher sample ratecompared with the bandwidth of the RF signal. Thus interference producedby the signals may appear to be white noise (e.g., signals with a flatspectral density rather than having discrete spurious components) in thebandwidth of the RF signal. In contrast, an analog envelope signal mayhave a similar bandwidth as the RF signal and tends to produce aspurious interference in the RF bandwidth. The interference becomes morelike white noise with increasing sample rate. In some cases, as thesample rate increases, the spectral density may become closer to that ofa white noise signal. Thus, even though the LVDS lines connecting thetransceiver 13 and the ET FEM 430 may produce interference due, forexample, to a transmission line effect, the interference tends to causeless degradation to the envelope-tracking signal 408 and/or the RFsignals compared to a conventional design that transmits an analogenvelope signal from a transceiver to an FEM. The RF signal, beforebeing amplified by the power amplifier 17 a, may be especially sensitiveto spurious interference because of, for example, the relatively lowpower level compared to post-amplification. Thus, having LVDS lines 420carrying oversampled LVDS signals from the transceiver 13 to the ET FEM430 can help to maintain the integrity of the RF signal. Similarly, in aMIMO system, interference produced by the LVDS lines going to one ET FEMtends to cause less degradation to the envelope-tracking signal 408 orthe RF signals of another ET FEM when compared with that of a designwherein analog envelope signals are transmitted from a transceiver to aplurality of FEMs instead of the LVDS signals. In addition, a largerbandwidth can be supported compared to systems that use analog envelopesignals.

Further, by using digital signals to represent and transmit the envelopeinformation, the size of the transceiver 13 or the ET FEM 430 can bereduced compared to systems that use an analog representation of theenvelope signal. By staying within the digital realm, the DACs and ADCsin the envelope tracking system can be reduced or eliminated.

The clock signal 418 may also generate interference on an RF signaland/or the envelope-tracking signal 408 because some electrical couplingmay occur within the transceiver 13 or within the communicationsubsystem 400. But because the clock signal 418 may operate at a muchhigher sample rate compared with the bandwidth of the RF signals and theenvelope-tracking signal 408, interference the clock signal 418 mayproduce on these signals can appear like white noise as well. Thus, theinterference produced by the clock signal 418 tends to cause lessdegradation to the RF signals and the envelope-tracking signal 408 whencompared with that of a conventional design wherein an analog envelopesignal is transmitted from a transceiver to an FEM.

In the ET FEM 430, a 1-bit D/A 422 may convert the LVDS signals to ananalog signal. Advantageously, in certain embodiments, a single-bit datastream can be recovered without a clock signal or a separate clocksignal. In particular, a sigma-delta bit stream may be recovered bylow-pass filtering the analog signal generated by the 1-bit D/A 422.Thus, in some cases, the analog envelope-tracking signal can berecovered without routing the clock signal generated by clock 418 fromtransceiver 13 to ET FEM 430. Not routing the clock signal to the ET FEM430 can eliminate a source of spurious interference, which may bepresent in some systems. Such spurious interference is undesirable in anRF system because, for example, the interference power at thefundamental frequency and the harmonics of the clock may causedegradation to the RF signal.

As discussed above, but not shown in FIG. 4, the D/A 422 may be followedby a low-pass filter (LPF) for data recovery. Alternatively, an LPF maybe included as part of the D/A 422. This LPF may also shape the analogenvelope-tracking signal to a bandwidth comparable to the bandwidth ofthe RF signal.

The output of the D/A 422 may be input to a driver 424. Driver 424 cangenerate an envelope-tracking signal 426 of sufficient power to functionas a supply to the power amplifier 17 a without causing the RF signal tobe clipped. The envelope-tracking signal 426 may be electricallyconnected to the supply of the power amplifier 17 a through a capacitor.The supply of the power amplifier 17 a may also be electricallyconnected to a DC-to-DC converter (DC/DC) through an inductor.

Advantageously, in certain embodiments, the baseband signal may be usedboth to generate the RF signal for transmission and to perform envelopetracking. The envelope tracking may be used to adjust the power consumedby the power amplifier. Thus, in contrast to traditional wirelessdevices that maintain the power amplifier at the maximum supportedpower, embodiments herein can reduce power consumption by adjusting thepower supplied to the power amplifier based at least in part on theenvelope information derived from the baseband signal.

Another Example Envelope Tracking System

FIG. 5 illustrates another block diagram of an embodiment of thecommunication subsystem 500 including an envelope tracking system. Theillustrated transceiver 13 includes a baseband processor 402, an I/Qmodulator 404, a signal estimation component 512, an LUT 514, adelta-sigma modulator 416, an LVDS driver 518, and a feedback(observation) receiver 506, which may include an A/D 508 and a mixer510. The communication subsystem 500 additionally includes a poweramplifier 17 a, an envelope tracker 434, a directional coupler 514, anantenna tuner 516, an antenna 14, and a controller 18.

As discussed above, the baseband processor 402 can generate an I signalcomponent and a Q signal component. The I/Q modulator 504 can beconfigured to receive the I and Q signals from the baseband processor402 and to process the I and Q signals to generate an RF signal. Thesignal estimation component 512 may be implemented as any system thatcan determine an approximate amplitude of the baseband I/Q signals.Further, the signal estimation component 512 may be implemented inhardware, software, or a combination of hardware and software. Incertain embodiments, as illustrated in FIG. 5 the signal estimationcomponent 512 may implement a CORDIC algorithm. For example, the signalestimation component 512 may implement the following algorithm:CORDIC(SQR(I^2+Q^2)). CORDIC stands for COordinate Rotation DigitalComputer and may also be referred to as the digit-by-digit method orVolder's algorithm. CORDIC is an algorithm to calculate trigonometricfunctions which does not have to use multiply operations.

The output of the signal estimation component 512 may be provided to adriver 520. The driver 520 can amplify the signal received from thesignal estimation component 512. This signal includes informationassociated with the baseband signal, such as the instantaneous amplitudeof the baseband signal. The amplified signal may be provided to the LUT514. Further, the driver 520 can provide the amplified signal, or acontrol signal based on the amplified signal, to a digitalpre-distortion (DPD) element of the I/Q modulator 404.

The LUT 514 can be used to convert an amplitude signal associated withthe I and Q signals (e.g., the output of the signal estimation component512) into a shaped envelope signal. In some cases, the content of theLUT may be dependent upon the implementation of the amplitude estimator.For example, the content of the LUT 414 may be different from that ofthe LUT 514 because LUT 414 receives its input from a signal estimationcomponent 414 that implements a vector length function, whereas LUT 514receives its input from a signal estimation component that implements aCORDIC function. In some cases, such as when the output of the signalestimation component 412 matches that of the signal estimation component512, the content of the LUT 414 may be the same as that of the LUT 514.

The delta-sigma modulator 416 can encode the envelope signal using asingle bit encoding. This single-bit encoding may be performed byapplying delta-sigma modulation to the envelope signal output from LUT514. The LVDS driver 518 can convert the output of the delta-sigmamodulator 416 to the LVDS format. The output of the LVDS driver 518 canbe transmitted on lines 420 to envelope tracker 434. In certainimplementations, the envelope tracker 434 comprises a 1-bit D/A and adriver. The envelope tracker 434 may receive a voltage from a batteryVbat and may can modify the Vbat voltage based on the LVDS output 420 togenerate the envelope-tracking voltage V_(CC) _(_) _(PA) _(_) _(trck).Envelope tracker 434 can supply the envelope-tracking voltage V_(CC)_(_) _(PA) _(_) _(trck) to the power amplifier 17 a. V_(CC) _(_) _(PA)_(_) _(trck) for the power amplifier 17 a may change in relation to theshaped envelope signal. The power amplifier 17 a can generate the outputsignal RF_out by amplifying the input signal RF_in. The RF_out signalmay propagate to the antenna 14 via a directional coupler 514 (whosefunction is described below) and an antenna tuner 516. The RF signal canbe then transmitted to a desired destination (e.g., a base station) viaantenna 14.

The directional coupler 514 can be positioned between the output of thepower amplifier 17 a and the input of the switches 12 (not shown) or theinput of the antenna tuner 516, thereby allowing an output powermeasurement of the power amplifier 17 a that does not include insertionloss of the switches 12 or the antenna tuner 516. The sensed outputsignal from the directional coupler 514 can be provided to the mixer510, which can multiply the sensed output signal by a reference signalof a controlled frequency (not illustrated in FIG. 5) so as to downshiftthe frequency spectrum of the sensed output signal. The downshiftedsignal can be provided to the ADC 508, which can convert the downshiftedsignal to a digital format suitable for processing by the basebandprocessor 402. By including a feedback path between the output of thepower amplifier 17 a and an input of the baseband processor 402, thebaseband processor 402 can be configured to dynamically adjust the I andQ signals and/or envelope signal associated with the I and Q signals tooptimize the operation of the communication subsystem 500. For example,configuring the communication subsystem 500 in this manner can aid incontrolling the power added efficiency (PAE) and/or linearity of thepower amplifier 17 a.

Typically, the transmit RF frequency is selected based on a control orcommand received from a base station. However, in some cases, thecommunication subsystem 500 may select a transmit RF frequency based onuser input or a command from the wireless device 11. Alternatively, thecommunication subsystem 500 may select a transmit RF frequency based onthe power level indicated through the coupler 514. The controller 18 cancontrol the transmit RF frequency through control signals to the I/Qmodulator 404 and the antenna tuner 516.

Another Illustration of an Envelope Tracking System

FIG. 6 is another illustration of an envelope tracking system 600. Asillustrated, the output 426 of the envelope tracker 434 is electricallyconnected to a DC-to-DC converter device through a capacitor and aninductor. Through these connections, the envelope tracker 434 modifiesthe DC-to-DC converter output 410 to generate an envelope-trackingsupply voltage V_(CC) _(_) _(PA) 408. Also as illustrated in FIG. 6, atime-varying RF signal can be input to the power amplifier 17 a. Thepower amplifier 17 a can receive an envelope-tracking supply voltageV_(CC) _(_) _(PA) 408 and can output a time-varying amplified RF signal.The power of the amplified RF signal may vary, for example, depending onthe distance between the communication subsystem 600 and the receivingdevice, such as a cellular base station receiver or a Wifi hotspotreceiver. Thus it may be desirable to produce the envelope-trackingsupply voltage V_(CC) _(_) _(PA) 408 based on the real-time variationsof the amplified RF signal.

As with the envelope tracking systems depicted in FIGS. 5 and 6, thesystem 600 may include a baseband processor 402 that provides a signalto the envelope tracking system 432. The baseband signal can be used toadjust the power supplied to the PA 17 a. Further, the basebandprocessor 402 may provide I and Q components of the baseband signal tothe I/Q modulator 404 to generate an RF signal for transmission.

Envelope Tracking System in a Wireless Device with Multiple Front-EndModules

FIG. 7 illustrates a communication subsystem 700 comprising atransceiver 13 and a plurality of FEMs 430 a-430 n. Neither the numberof FEMs (or their components) illustrated in FIG. 7 nor their referencenumbers (e.g., 430 a-430 n) is meant to be limiting. A communicationsubsystem 700 may have any number of FEMs. In the remainder of thedisclosure, an FEM in a wireless device may be individually referred toas FEM 430 a, FEM 430 b, etc., or may be individually or collectivelyreferred to as FEM 430.

In FIG. 2, one or more output signals from the transceiver 13 aredepicted as being provided to the antenna 14 via one or moretransmission paths 15. As described above relative to FIG. 2, differenttransmission paths 15 can represent output paths associated withdifferent bands and/or different power outputs. FIG. 7 illustrates anembodiment wherein the different transmission paths 15 a-15 n representpaths associated with different FEMs 430. Each FEM may have its ownenvelope tracker 434 and its own power amplifier 17. Further, each FEMmay have its own transmission path 15 for the RF signal, and its owntransmission path 420 for the LVDS signal. The RF signal input to onepower amplifier may be different from the RF signal input to anotherpower amplifier. Likewise, the LVDS signal input to one envelope tracker434 may be different from the LVDS signal input to another envelopetracker 434. Thus, a plurality of transmission paths 15 and 420 mayexist between the transceiver and the plurality of FEMs.

As discussed above, the different FEMs may be used in a MIMO system andmay be spatially separated, leading to different path delays andfrequency responses among paths 420 a-420 n. Advantageously, in certainembodiments, the degradation effects due, for example, to the differentpath lengths between the transceiver and the FEMs are reduced oreliminated compared with a conventional design because, for example, ofthe use of the single-bit LVDS signals as described above.

In some cases, signals communicated or electrically communicated via thepaths 15 and 420 may cause mutual interference. For example, a signalpath 420 a may cause interference on another signal path, such as path15 b. This interference may cause distortion to the RF input signalbecause, for example, RF input signals are typically low-power signals.The RF input signals may be around 10 dBm, but can reach as low as −70dBm. Typically, the LVDS signals are substantially close to 0 dBm.Advantageously, in certain embodiments, the degradation caused bycross-path interference may be reduced or eliminated compared with aconventional design because, for example, of the use of the single-bitLVDS signals as described above.

In operation, each FEM may transmit in one or more of a plurality of RFfrequency bands. Furthermore, each FEM may not always transmit in afixed frequency band. For example, FEM 430 a may transmit usingfrequency band #1 at one time and transmit using frequency band #2 atanother time. Thus the look-up table 414 may contain a plurality ofmapping tables for each FEM, with each mapping table designated for aparticular FEM transmitting using a particular RF frequency band. Inoperation, one table may be active for each FEM based on its transmit RFfrequency band.

Example Envelope-Tracking Supply—Voltage Determination Process

FIG. 8A presents a flowchart of an embodiment of an envelope-trackingsupply voltage determination process 800. The process 800 can beimplemented by any system that can configure a power amplifier supplyvoltage based, at least in part, on the RF signal voltage being used tocommunicate with another device, such as a cellular base station. Forexample, the process 800 may be performed by a signal estimationcomponent 412, a signal estimation component 512, a look-up table suchas LUT 414 or 514, a sigma-delta modulator 416, a clock 418, and a LVDSdriver 518. Although one or more systems may implement the process 800,in whole or in part, to simplify discussion, the process 800 will bedescribed with respect to particular systems.

The process 800 begins at the block 802 where, for example, a signalestimation component 412 receives an I/Q baseband signal from a basebandprocessor 402. At block 804, the signal estimation component canestimate or measure the magnitude of the I/Q baseband signal. Asdiscussed above, this estimate or measurement may be implemented in avariety of ways such as using a vector length function or a CORDICfunction. Additionally, some systems may compute the magnitude of theI/Q baseband signal in the baseband processor. In such systems, thebaseband processor can output the magnitude directly to the envelopetracking system 432.

At block 806, the envelope tracking system can determine an RF envelopeamplitude based on the I/Q signal magnitude. This may be done via alook-up table, such as LUT 414 or LUT 514. The I/Q signal magnitude andRF envelope amplitude may be represented as a digital word of a numberof bits, e.g., 8 or 12 bits. The relatively small number of bits canpermit an efficient implementation of a look-up table as the size of thetable can be proportional to the number of digital states, e.g., 2^8 or256 for an 8-bit word.

At block 808, the envelope tracking system may use a delta-sigmamodulator 416 to convert the multi-bit RF envelope signal to a singlebit. To maintain the information in the multi-bit signal using a singlebit, the delta-sigma modulator may output a single-bit data signal at anoversample clock rate. A clock source 418 may be used to supply a clocksignal to the delta-sigma modulator.

At block 810, the envelope tracking system may convert the single-bitdata signal to an LVDS format. The system may include an LVDS driver 518to perform this conversion. The system can transmit the LVDS-formattedsignal to one or more front-end modules at block 812.

Example Envelope-Tracking Supply-Voltage Supply Process

FIG. 8B presents a flowchart of an embodiment of an envelope-trackingsupply voltage supply process 850. Like process 800, the process 850 canbe implemented by any system that can configure a power amplifier supplyvoltage based, at least in part, on the RF signal voltage being used tocommunication with another device, such as a cellular base station. Insome cases, the processes 800 and 850 can represent two complementaryprocesses to generate an envelope-tracking power supply voltage. As anexample, the process 850 may be performed by a one-bit D/A 422 and/or adriver 424. The output of the driver 424 can be an envelope-trackingsupply voltage to a power amplifier 17 a. Although one or more systemsmay implement the process 850, in whole or in part, to simplifydiscussion, the process 850 will be described with respect to particularsystems.

The process 850 starts at block 852 where, for example, an envelopetracker 434 may receive an LVDS signal from a transceiver 13. At block854, the envelope tracker converts the LVDS signal to an analog envelopetracking signal. This conversion may be performed using a one-bit D/A422. The one-bit D/A 422 may use a low pass filter to filter the signalbased at least in part on the bandwidth of the envelope of the RFsignal. In certain embodiments, the analog envelope tracking signalproduced in block 854 can be correlated, in the time domain forinstance, to the RF envelope amplitude signal produced in block 806.

At block 856, the envelope tracker 434 conditions the analog envelopetracking signal based on the power amplifier 17 a. Conditioning theanalog envelope tracking signal may involve, for example, boosting thecurrent level to a level which may be required by a particularimplementation of a power amplifier. As another example, the process inblock 856 may involve offsetting and/or scaling the voltage of theanalog envelope tracking signal to satisfy the supply voltage rangewhich may be required by the particular implementation of the poweramplifier. At block 858, the system can supply the conditioned envelopetracking signal to a power amplifier.

Example Delta-Sigma Modulator Output and Envelope Tracking SupplyVoltage

FIG. 9 illustrates a graph 900 of the output of the delta-sigmamodulator 902 (thin line with dotted areas) and the correspondingenvelope-tracking signal 904 (thick line). The delta-sigma modulatoroutput 902 may be associated with either a logical zero or a logicalone. The logical state at a particular sample may depend on the slope ofthe corresponding envelope-tracking signal 904 as discussed above. Incases where the slope has frequent polarity changes, the delta sigmaoutput 902 can oscillate quickly between the two logic states. On graph900 with a compressed time axis, such quick oscillations appear to forma cluster, represented with dotted areas enclosed by a thin line. Forexample, a cluster appears around Time=1.0419 milliseconds. The voltagesof the logic zero and one states of the delta-sigma modulator output maybe scaled. In graph 900, the delta-sigma modulator 902 is scaled betweenabout 1.25 V to over 6 V. The scaling may be done such that the envelopetracking system produces an envelope tracking signal 904 with a voltagerange that satisfies the voltage required by a particular implementationof a power amplifier.

Example Ideal and Achieved Envelope Tracking Supply Voltage

FIG. 10 illustrates a graph 1000 showing an ideal envelope trackingsignal 1002 (solid line) and an envelope tracking signal achievablethrough a certain embodiment 1004 (dotted line). Although the twosignals 1002 and 1004 are not identical in shape, the differences may beattributed to various sources of error in the envelope tracking system,for example magnitude estimation or measurement error. However, thegraph 1000 illustrates that the achievable output 1004 tracks closelythe ideal output 1002 demonstrating that certain embodiments herein canbe used to generate an envelope-tracking signal while achieving theadvantages described herein.

Example Spectral Density

FIG. 11 illustrates a graph 1100 of spectral densities versus frequency.Curve 1102 (thin solid line) is spectral density of an example RF signalamplified through a power amplifier with an ideal envelope trackingsupply voltage. Curve 1104 (dotted line) is the spectral density of thesame example RF signal amplified through a power amplifier with anenvelope tracking signal achievable through a certain embodiment. Line1106 (thick solid line) shows an example spectral density requirementwhich may be imposed by a certain communication system or standard. Thetwo spectral densities 1102 and 1104 are not identical in shape. Asdescribed above in relation to FIG. 10 above, the differences may beattributed to various sources of error in the envelope tracking system,for example magnitude estimation or measurement error. However, theshowing that the achievable spectral density 1104 tracks closely theideal spectral density 1102 demonstrates that certain embodimentsdescribed herein can be used to generate a good envelope-trackingsignal.

One measure of a “good” envelope-tracking signal may be whether theresulting RF spectral density, such as curve 1104, meets the spectraldensity requirements which may be imposed by a certain communicationsystem or standard, e.g., line 1106. The line 1106 may represent a powerrequirement within the RF bandwidth, e.g. about −50 dBm/Hz from about−15 MHz to +15 MHz. The line 1106 may also represent adjacent channelrejection requirements, e.g. about −95 dBm/Hz from about 30 to 50 MHzaway from the center of the RF channel (shown in graph 1100 as 0 Hz),and about −103 dBm/Hz from about 50 MHz to 170 MHz away from the centerof the RF channel. As illustrated in graph 1100, the curve 1104 meetsthese spectral density requirements which may be imposed by a certaincommunication system or standard. Thus the envelope tracking signal maybe considered “good.”

Terminology

It is to be understood that not necessarily all objects or advantagesmay be achieved in accordance with any particular embodiment describedherein. Thus, for example, those skilled in the art will recognize thatcertain embodiments may be configured to operate in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other objects or advantages as maybe taught or suggested herein.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The term “coupled” is used to refer tothe connection between two elements, the term refers to two or moreelements that may be either directly connected, or connected by way ofone or more intermediate elements. Additionally, the words “herein,”“above,” “below,” and words of similar import, when used in thisapplication, shall refer to this application as a whole and not to anyparticular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

The above detailed description of embodiments of the inventions are notintended to be exhaustive or to limit the inventions to the precise formdisclosed above. While specific embodiments of, and examples for, theinventions are described above for illustrative purposes, variousequivalent modifications are possible within the scope of theinventions, as those skilled in the relevant art will recognize. Forexample, while processes or blocks are presented in a given order,alternative embodiments may perform routines having steps, or employsystems having blocks, in a different order, and some processes orblocks may be deleted, moved, added, subdivided, combined, and/ormodified. Each of these processes or blocks may be implemented in avariety of different ways. Also, while processes or blocks are at timesshown as being performed in series, these processes or blocks mayinstead be performed in parallel, or may be performed at differenttimes.

The teachings of the inventions provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

Conditional language used herein, such as, among others, “can,” “might,”“may,” “e.g.,” and the like, unless specifically stated otherwise, orotherwise understood within the context as used, is generally intendedto convey that certain embodiments include, while other embodiments donot include, certain features, elements and/or states. Thus, suchconditional language is not generally intended to imply that features,elements and/or states are in any way required for one or moreembodiments or that one or more embodiments necessarily include logicfor deciding, with or without author input or prompting, whether thesefeatures, elements and/or states are included or are to be performed inany particular embodiment.

Disjunctive language such as the phrase “at least one of X, Y, or Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to present that an item, term, etc., may beeither X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z).Thus, such disjunctive language is not generally intended to, and shouldnot, imply that certain embodiments require at least one of X, at leastone of Y, or at least one of Z to each be present.

Unless otherwise explicitly stated, articles such as “a” or “an” shouldgenerally be interpreted to include one or more described items.Accordingly, phrases such as “a device configured to” are intended toinclude one or more recited devices. Such one or more recited devicescan also be collectively configured to carry out the stated recitations.For example, “a processor configured to carry out recitations A, B andC” can include a first processor configured to carry out recitation Aworking in conjunction with a second processor configured to carry outrecitations B and C.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. An envelope tracking system comprising: a signalmeasuring device configured to determine a size of a radio frequencyinput signal; a bit-encoder configured to encode an envelope trackingcontrol signal to obtain an encoded envelope tracking control signal,the envelope tracking control signal based at least in part on the sizeof the radio frequency input signal, the signal measuring device and thebit-encoder included in a transceiver; and an envelope trackerconfigured to provide a supply voltage to a power amplifier, the supplyvoltage based at least in part on the encoded envelope tracking controlsignal, the envelope tracker included in a radio frequency front endmodule that is separate from the transceiver and communicates with thetransceiver via a pair of low-voltage digital differential signalinglines.
 2. The envelope tracking system of claim 1 wherein the signalmeasuring device determines the size of the radio frequency input signalby determining an amplitude of I and Q components of a baseband signalassociated with the radio frequency input signal.
 3. The envelopetracking system of claim 2 wherein determining the amplitude of theradio frequency input signal includes obtaining the absolute value ofthe amplitude of the I and Q components associated with the radiofrequency input signal.
 4. The envelope tracking system of claim 1wherein the signal measuring device implements a coordinate rotationdigital computer algorithm.
 5. The envelope tracking system of claim 1wherein the bit-encoder includes a sigma-delta modulator.
 6. Theenvelope tracking system of claim 1 further comprising a lookup tablestoring a plurality of envelope tracking control values.
 7. The envelopetracking system of claim 6 wherein the envelope tracking control signalis generated based at least in part on the size of the radio frequencyinput signal or a selection of an envelope tracking control value fromthe plurality of envelope tracking control values.
 8. The envelopetracking system of claim 1 further comprising the pair of low-voltagedigital differential signaling lines configured to communicate theencoded envelope tracking control signal from the bit-encoder to theenvelope tracker.
 9. The envelope tracking system of claim 1 wherein theenvelope tracker includes a digital to analog converter configured toconvert the encoded envelope tracking control signal to an analogsignal.
 10. The envelope tracking system of claim 1 wherein the envelopetracker includes a driver configured to generate the supply voltage. 11.The envelope tracking system of claim 1 wherein the size of the radiofrequency input signal includes an instantaneous amplitude of the radiofrequency input signal.
 12. The envelope tracking system of claim 1wherein the radio frequency front end module is one of a plurality ofradio frequency front end modules in communication with the transceiver.13. The envelope tracking system of claim 1 where in the transceiver isspatially separated from at least one of the plurality of radiofrequency front end modules resulting in different length low-voltagedigital differential signaling lines between the transceiver and atleast one of the plurality of radio frequency front end modules.
 14. Awireless device comprising: a transceiver including a signal measuringdevice and a bit-encoder, the signal measuring device configured todetermine a size of a radio frequency input signal, and the bit-encoderconfigured to encode an envelope tracking control signal to obtain anencoded envelope tracking control signal, the envelope tracking controlsignal based at least in part on the size of the radio frequency inputsignal; and a radio frequency front-end module in communication with thetransceiver, the radio frequency front-end module including an envelopetracker configured to provide a supply voltage to a power amplifier, thesupply voltage based at least in part on the encoded envelope trackingcontrol signal, the wireless device including a plurality of radiofrequency front-end modules, at least one of the radio frequencyfront-end modules including one or more power amplifiers configured toprocess signals of a different frequency band than at least one other ofthe radio frequency front-end modules, the plurality of radio frequencyfront-end modules being in communication with the transceiver via aplurality of pairs of low-voltage digital differential signaling lines,and at least one of the pairs of low-voltage digital differentialsignaling lines being of a different length than at least one other pairof low-voltage digital differential signaling lines.
 15. The wirelessdevice of claim 14 wherein the bit-encoder includes a sigma-deltamodulator.
 16. The wireless device of claim 14 wherein the transceiverfurther includes a non-volatile storage configured to store a mapping ofa plurality of radio frequency input size values to a plurality ofenvelope tracking control values.
 17. The wireless device of claim 16wherein the envelope tracking control signal is determined based atleast in part on the size of the radio frequency input signal and themapping of the plurality of radio frequency input size values to theplurality of envelope tracking control values.
 18. The wireless deviceof claim 14 wherein the envelope tracker includes a digital to analogconverter configured to convert the encoded envelope tracking controlsignal to an analog signal.
 19. The wireless device of claim 14 whereinthe envelope tracker includes a driver configured to modify a voltagereceived from a battery to obtain the supply voltage for the poweramplifier.
 20. A method of envelope-tracking a radio frequency signal,the method comprising: receiving I and Q components of a radio frequencysignal at a modulator of a transceiver; determining an expected size ofthe radio frequency signal based on a measurement of the I and Qcomponents; determining a control signal based at least in part on theexpected size of the RF signal, the control signal indicating a voltageenvelope for the radio frequency signal; converting the control signalto a low-voltage digital differential signaling format using a digitalbit encoder to obtain an encoded control signal; and transmitting via apair of low-voltage digital differential signaling lines the encodedcontrol signal to an envelope tracker of a radio frequency front-endmodule that is on a separate die from the transceiver.
 21. The method ofclaim 20 wherein, in response to providing the encoded control signal tothe envelope tracker, the method further comprises: modifying a devicesupply voltage based at least in part on the encoded control signal; andproviding the modified device supply voltage to a power amplifier thatreceives the radio frequency signal.